1. Field of the Invention
The present invention relates to a measuring apparatus for use in a recording unit, in particular, to a measuring apparatus for measuring performance characteristics of a recording unit including a recording medium of a hard disk, a floppy disk, or an optical disk such as CD, DVD, a magneto-optical disk (of ROM, write once type, rewriting type) or the like and components such as a head for recording a data signal on the above recording medium and the like.
2. Description of the Prior Art
Upon testing either a fixed type magnetism fixture magnetic disk drive unit (referred to as a hard disk unit hereinafter) for driving a hard disk, the above hard disk, or a magnetic head, there is the practice of evaluating the performance characteristics of the above hard disk, the testing process includes the following steps:
(a) inserting a spindle into a center hole of the hard disk and supporting the magnetic head so as to electromagnetically couple the magnetic head with the surface of the hard disk in a non-contact manner;
(b) executing either a data writing process or a data reading process on the hard disk by means of the magnetic head while rotating the spindle by means of a spindle motor; and
(c) evaluating the performance characteristics of the hard disk unit including the hard disk.
As performance evaluation items, the following ones can be enumerated. The performance evaluation items includes the followings:
(a) a track average signal amplitude (Track Averaged Amplitude: referred to as a TAA hereinafter);
(b) an asymmetry of a signal amplitude;
(c) a pulse width (PW);
(d) an asymmetry of a pulse width;
(e) a base line;
(f) a non-linear type bit shift amount (Non-linear Transition bit shift: NLTS);
(g) an overwrite characteristic (OverWrite: OW);
(h) a bit error rate (Bit Error Rate: BER);
(i) a margin, and so on.
The evaluation items of the TAA for a read signal from the hard disk are shown in FIG. 10.
When evaluating the performance of a hard disk, it is required to set parameters for measurement, and the parameters includes the followings:
(a) a position of a magnetic head (referred to as a head position hereinafter);
(b) a head angle (skew);
(c) a spindle rotation speed;
(d) a signal frequency;
(e) a write data pattern;
(f) a write current amount;
(g) a write compensation amount (concretely, a amount of compensation for compensating for the write change timing);
(h) an MR (Magnetic Resistance) head bias current, and so on.
In this case, the signal frequency, the write data pattern, the write current amount, the write compensation amount, the head position and the MR head bias current are write parameters for the hard disk, while the head position, the head angle and the MR head bias current are read parameters for the hard disk.
A procedure in measuring the above evaluation items has a sequence of parameter setting, writing onto a disk, reading out and evaluating the characteristics of the read signal. FIG. 11 shows signal waveforms of a write signal and a read signal. Conventionally, it has been a common practice to obtain a parameter dependency of the measured values of the evaluation items by changing set values of the above-mentioned parameters in small steps and repetitively executing a similar measurement.
For example, FIG. 12 shows a dependency of the TAA on a write current amount Iw. According to the conventional technique, such a measurement has been executed by writing data with fixed one parameter for one rotation of the disk when the spindle is rotated by one turn, and reading out the written data during another turn, thereby obtaining the measurement data for one point in FIG. 12. By repeating this sequence a plurality of times while changing the parameter, a graph as shown in FIG. 12 is obtained according to the measuring method based on the conventional technique (referred to as a first prior art hereinafter). That is, according to the conventional technique, one parameter has been set per one revolution of the track.
There is sometimes such a case that the state of a read element is disadvantageously changed by a magnetic field in the writing stage, then consequently, this leads to an unstable characteristic (referred to as instability hereinafter). This phenomenon may be a kind that occurs only once per several times or another kind that occurs as a variation every measurement. Therefore, in measuring such a characteristic, it is a common practice to repeat the write and read operations many times, and then statistically evaluate the measured values of read signals. When measuring the above-mentioned instability by a conventional technique (referred to as a second prior art hereinafter), statistic data including the average value and the variance of the measured value data are obtained, as shown in FIG. 13, by executing a plurality of times, a process including the steps of, first of all, writing desired data on the whole track of the disk, writing data which will be abandoned for a part of the track, and thereafter reading out the data on the rest of the track.
The above-mentioned prior art measuring method and measuring apparatus have had such a problem that the measuring time is relatively long.
Furthermore, when executing the measurement by switching the measurement item upon evaluating the performance characteristics of a hard disk, it takes much measuring time according to the prior art methods in an attempt at viewing the influences on the parameters requiring a significantly long time for convergence. As the parameters requiring a significantly long time for convergence, there can be enumerated the frequency, the head position and so on. For example, FIG. 21 shows a relationship between the head position and the read signal amplitude, where the relationship is called the track profile. Such a measurement (referred to as a third prior art hereinafter) takes a long time for moving the head position as compared with that of the rotation of the spindle, and this leads to such a problem that the measuring time is elongated.